In Humans,the Allele N Causes an Abnormal Shape of the Patella

Essay

In humans,the allele N causes an abnormal shape of the patella in the knee (n is the normal allele).A separate gene is concerned with finger length,and the allele B causes abnormally short fingers,whereas b gives normal length.A study focused on people who have both abnormal patellae and short fingers (they were most likely N/n ^. B/b in genotype),having inherited the N allele from one parent and the B allele from the other parent.These N/n ^. B/b people mated with normal spouses,producing 40 progeny classified as follows:
$$\begin{array} { l l } \text { Normal } & 3 \\\text { Abnomal knees and fingers } & 2 \\\text { Abromal knees only } & 17 \\\text { Abnomal fingers only } & 18\end{array}$$
a)Draw the chromosomes of the N/n ^. B/b individuals,their parents,and their four types of children,showing the positions of the alleles.
b)Explain why the four types of children were in the proportions shown.